Ethylene-propylene-diene rubbers (EPDM) are rubbers excellent in weather resistance, ozone resistance and thermal aging resistance and widely used for the static sections of automobile parts, such as weather stripping, door glass run channel, radiator hose, etc.
On the other hand, most of parts such as tires, rubber vibration insulators, etc. which require mechanical strength against dynamic fatigue are prepared by using conjugated diene rubbers such as NR, SBR and BR or blends thereof.
It is necessary to improve the thermal aging resistance and weather resistance of automobile parts to cope with the improved performance of automobiles in recent years.
However, though EPDM is excellent in weather resistance, ozone resistance and thermal aging resistance, dynamic fatigue resistance thereof is so poor that EPDM alone cannot be used for the preparation of tires and rubber vibration insulators.
Accordingly, there have been made many studies on the blends of EPDM and the conjugated diene rubber to utilize the advantageous characteristics of each of EPDM and conjugated diene rubber. However, EPDM-conjugated diene rubber blends excellent in co-vulcanizability could not be obtained and hence they could not be put to practical use.
Conventional techniques related to the blends of EPDM and conjugated diene rubber in the above studies are described in Journal of the Society of Rubber industry, Japan, 51,685 (1978) written by Yasuhiro Oda and Masashi Aoshima. As the blending techniques, there are disclosed (1) vulcanization with polysulfides, (2) vulcanization with peroxides, (3) application of prevulcanized EPDM, (4) application of prevulcanized EPDM having a high iodine value, (5) application of halogenated EPDM, (6) utilization of accelerators having a long-chain alkyl group, etc.
According to the disclosures of the aforesaid literature, EPDM having an intrinsic viscosity of at least 3.0 dl/g as measured in xylene at 70.degree. C., a propylene content of not higher than 35% and a high iodine value is found to be good.
Though these descriptions are directed to improve the co-vulcanizability of EPDM with conjugated diene rubber, however, there is described nothing about the items of quality practically required for the quality of goods, particularly about dynamic strength. EPDM-conjugated diene rubber having excellent dynamic fatigue resistance could not be obtained by the above-described techniques.
The purpose of blending EPDM with conjugated diene rubber is to impart excellent thermal aging resistance and weather resistance to the resulting blends without reducing practically excellent crack growth resistance, dynamic fatigue resistance and wear resistance which conjugated diene rubbers possess. Accordingly, it is necessary that dynamic fatigue resistance is imparted to EPDM to be blended with conjugated diene rubbers.
As an example of requiring dynamic fatigue resistance most, there is described in Rubber Chemistry Technology, Vol. 44, page 1043 (October 1971) that the desired characteristics can be obtained by using EPDM having a high Mooney viscosity for All-EPDM as a rubber vibration insulator.
However, the use of high-molecular-weight EPDM is considered to be a matter which is easily conceived by those skilled in the art. The most essential point of research and development is to improve physical properties of the resulting blend without detriment to the processability of the blend. The processability of EPDM decreases when the molecular weight of EPDM increases. Any means for improving simultaneously both the processability and the dynamic fatigue resistance has not been disclosed as yet. A known technique to improve the processability of EPDM having a high Mooney viscosity is to extend EPDM with paraffinic or naphthenic extender oil. However, an elastomer composition containing an ethylene-propylene-diene rubber (EPDM) having excellent co-vulcanizability could not be obtained without deteriorating the excellent wear resistance and dynamic fatigue resistance which conjugated diene rubbers possess, by using merely the extender oil.
Accordingly, it has been demanded to provide ethylene-propylene-diene rubber, an elastomer composition containing said ethylene-propylene-diene rubber and vulcanized rubber composed of said elastomer composition, said ethylene-propylene-diene rubber being excellent in co-vulcanizability with conjugated diene rubbers and being capable of imparting excellent weather resistance, ozone resistance and thermal aging resistance without deteriorating the excellent mechanical characteristics, wear resistance and dynamic fatigue resistance which conjugated diene rubbers such as NR, IR, SBR and BR possess.
Japanese Patent Laid-Open Publn. No. 22551/1978 discloses a vulcanizable composition for a rubber vibration insulator having improved fatigue failure life comprising an ethylene-propylene rubber, which is obtained by adding 5 to 90 parts by weight of carbon black, 0.1 to 2 parts by weight of sulfur and a suitable amount of process oil to 100 parts by weight of oil-extended rubber composed of a mixture of a rubber with an extender oil, said rubber consisting of 10 to 50% by weight of an ethylene-propylene-ethylidene-norbornene terpolymer having an intrinsic viscosity [.eta.] of not higher than 1.0 as measured at 70.degree. C. in xylene solution and 90 to 50% by weight of an ethylene-propylene-ethylidene-norbornene terpolymer having an intrinsic viscosity [.eta.] of not lower than 3.0 as measured in the same manner as that described above, and said extender oil contained and amount of 20 to 80 parts by weight, based on 100 parts by weight of the rubber.
The present invention is intended to solve such problems associated with the prior art as mentioned above and an object of the present invention is to provide ethylene-propylene-diene rubbers, elastomer compositions containing said ethylene-propylene-diene rubber and vulcanized rubbers comprising said elastomer compositions, said ethylene-propylene-diene rubbers being excellent in co-vulcanizability with conjugated diene rubbers and being capable of imparting excellent weather resistance, ozone resistance and thermal aging resistance without deteriorating the excellent mechanical characteristics, wear resistance and dynamic fatigue resistance which conjugated diene rubbers such as NR, IR, SBR and BR possess.